In the past, a number of different types of dimmer switches have been known both for incandescent and fluorescent lighting systems. While the most common control for lights or lighting systems has been the on/off switch, manual dimmer switches have increased in popularity because of the flexibility they offer the user to control the lighting in a room to the desired and most comfortable intensity.
Such manually operated dimmer switches are readily available commercially and are well known in the art. These manually operated light dimmer switches typically control the brightness of the light by controlling the resistance of a manually operated variable resistor in the control circuit of a silicon controlled rectifier which in turn controls the amount of current to the electric light bulb and thereby controls the brightness or intensity of the light emitted. In addition, such prior art dimmer switches frequently also include an instant on-instant off capability.
The human eye requires approximately 15 minutes to fully adjust from a dark environment to a normal, well-lighted environment, or vice versa. Rapid changes from dark to normal lighting conditions causes unpleasant sensations in the human eye and indeed may even cause flash blindness in extreme cases. Upon going from light to near darkness, a person cannot see well until his eyes adjust. This condition can be particularly noticeable by a person developing film in a dark room, for example, where certain operations are performed in total darkness while others are performed at normal light intensity levels, or even by a person trying to locate a door or some other object, such as a bed, in a dark room after the light has been turned off. In addition, there are frequently periods of time after an eye operation when abrupt changes in light intensity from dark to bright could be very painful, if not harmful to the patient.
Further, it is often unpleasant and frequently more difficult for a person to awaken early in the morning before dawn and while it is still dark, than it is to awaken after dawn when the eye is partially adjusted to the light through the eyelid. A more natural method of awakening a person in a pleasurable manner is the gradual lighting of the area around the person as produced by the rising of the sun.
Unfortunately, commercially available dimmer switches, while capable of gradually increasing the light intensity, cannot do so in an automatic manner since an individual must gradually turn the control knob in order to gradually increase the intensity, giving rise to an inconvenience which would ordinarily prevent the dimmer switch from being used in this manner.
The prior art reveals a number of devices for gradually increasing the intensity of a light or gradually decreasing the intensity. For example, U.S. Pat. No. 3,798,889 discloses an artificial sun rise producing device which utilizes a tapered slit to control the amount of light reaching a light sensitive resistor for controlling the intensity of the lighting system.
More recently, a number of solid state devices such as triacs, diacs, programmable unijunction transistors, light emitting diodes, and the like have been used for controlling light dimmers in a progressively variable manner. Such devices are typified by U.S. Pat. Nos. 3,898,516, 4,008,416, 4,152,607, 4,152,608, 4,144,478, 4,159,442, 4,082,961, and 3,893,002.